1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a fused silica crucible, and the fused silica crucible, and more particularly, a technique using arc melting suitable for manufacturing a large-diameter crucible.
Priority is claimed on Japanese Patent Application No. 2008-244521, filed on Sep. 24, 2008, the content of which is incorporated herein by reference.
2. Description of the Related Art
A method of manufacturing a fused silica crucible by rotational molding is a method of manufacturing a fused silica crucible constituted by a transparent layer on the inside and an opaque layer on the outside by heating and melting a vitreous silica powder accumulated in a rotational mold by arc discharge. An existing configuration of electrodes for forming the arc discharge is disclosed in Japanese Patent No. 3647688 in which three electrodes are used, and an arc (discharge) plasma is formed between the electrodes through a three-phase alternating current.
As the diameters of pulled single crystal increase, there are demands for an increase in size of fused silica crucibles, such as those having a diameter of 32 inches or 40 inches, and an electrode configuration capable of forming an arc discharge with a wide heating range. An existing electrode configuration includes three three-phase electrodes, and when the distance between the electrodes is increased in order to expand the heating range, there is a problem in that the arc becomes unstable and broken. Particularly, in the case of a large crucible, the influence of an air flow on the inside of the crucible increases due to the rotation of the mold, so that the arc is more likely to be broken in the existing electrode configuration.
For this reason, a technique of increasing the number of electrodes is disclosed in JP-A-2003-335532.